1. Field of the Invention
This invention relates to a hydrophilic and thermoreactive urethane composition having improved properties, e.g., such as stability in solution, non-tackiness, water resistance and strength, or in other words, a urethane composition that contains stabilized isocyanate groups and is soluble in water or self-dispersible in water (hereinafter, this property of being self-dispersible in water will be referred to as "hydrophilic").
This invention also relates to a thermoreactive urethane aqueous adhesive composition comprising a hydrophilic and thermoreactive urethane composition.
This invention additionally relates to a process for producing an artificial leather having superior bond strength, water resistance, wash resistance and solvent resistance using a hydrophilic thermoreactive urethane composition.
This invention further relates to a method for finishing fibrous products using a treating liquor comprising a hydrophilic and thermoreactive urethane composition.
2. Description of the Prior Art
A number of aqueous urethane composition have been previously known. These urethane compositions are either those having anionic, cationic or nonionic hydrophilic groups in the polyurethane substrate in sufficiently large quantities that the compositions are rendered hydrophilic, or those in which the polyurethane substrate is emulsified using fairly large quantities of an emulsifying-dispersing agent. Accordingly, conventional urethane compositions suffer from the disadvantage that aqueous solutions or dispersions thereof have poor stability or give rise to difficulties such as gum-up, and polyurethanes obtained therefrom have unsatisfactory properties such as high tackiness, or poor water resistance and strength.
Further, in the past various adhesives have been utilized for many laminated materials or composite materials, and it is well known that polyurethane-type adhesives or the so-called polyisocyanate-type adhesives comprising urethane prepolymers or mixtures of polyisocyanates with active hydrogen-containing compounds are an example of such adhesives. These polyisocyanate-type adhesives have many characteristics such as high bond strength, superior water resistance and chemical resistance, and do not give off formaldehyde. Furthermore, depending upon the composition, these adhesives become elastic and flexible, and, therefore, are suitable for bonding parts which undergo bending and flexure. Thus, these adhesives have been used to bond various materials such as wood, fibrous materials, natural and synthetic rubbers, plastics, metals and glass. Many of these adhesives, especially polyurethane-type adhesives, require considerable amounts of solvent, and the danger of toxicity, fire, and explosion ascribable to the solvent is increased. Moreover, the use of a solvent degrades the working environment and the natural environment. A solvent sometimes is not required in a urethane prepolymer or a polyisocyanate mixture, but there still is the problem of toxicity due to vaporization of isocyanate monomer present in the composition. Furthermore, such an adhesive gels during storage for long periods of time or during treatment for long periods of time, and many difficulties, both of an economical nature and from the standpoint of efficiency, occur.
Emulsions obtained by specifically emulsifying polyurethane elastomers with an emulsifying-dispersing agent have been proposed. However, these polyurethane elastomers have poor stability, and most of them have inferior bond strength, water resistance and chemical resistance to the above-mentioned adhesives.
In view of this situation, extensive investigations have been made with a view to obtaining an aqueous urethane composition and an adhesive composition which can be used safely in an aqueous system continuously for long periods of time and stored for a long time, and also which has high bond strength and very superior water resistance and chemical resistance.
Further, in the production of artificial leather by bonding a sheet-like material capable of being used as a top-coat to a fabric capable of becoming a base, solvent solutions of polyurethane resins or urethane prepolymers having strong and elastic adhesive strength have frequently been used in the past. However, such a method involves high production cost because of the use of large quantities of solvent, and problems such as bad odor, toxicity or the danger of an explosion have been of concern. In using urethane prepolymers, solvents are not always required, but many operational difficulties such as a gellation of the prepolymers or the toxicity of isocyanate vapor have been encountered.
Attempts have been made to use aqueous adhesives of polyurethane emulsions obtained by emulsifying polyurethane resins or rendering them self-emulsifiable. However, these adhesives which have been emulsified have poor emulsion stability, and can not be stored for long periods of time. Furthermore, these adhesives gum-up during operation, and most of them have unsatisfactory bond strength, wash resistance and solvent resistance. These adhesives which are self-emulsifiable have good emulsion stability, but usually have extremely poor bond strength and especially, extremely poor water resistance and wash resistance.
It is also well known that polyurethane resins or urethane prepolymers, in the presence of solvents, can be applied to fibrous products. The fibrous products so finished have durable improved feel, stiffness, elastic recovery, crease resistance, shrink resistance, form retention, or anti-pilling property. However, a risk of toxicity or explosion exists in using solvents, and many problems are involved in the application of solvents. Furthermore, when urethane prepolymers are used, their solutions gel with time, and many operational difficulties occur.
Various polyurethane emulsions for enabling such a fibrous treating method to be carried out in an aqueous system are known. As described above, there are two types of polyurethane emulsions, self-emulsifiable polyurethane resins and positively emulsified polyurethane resins. The former type is still tacky because of its composition, and most species of this type can not impart stiffness and elastic recovery to fibrous products and have poor wash resistance. The latter type shows a considerable improvement over the former in regard to tackiness, stiffness, elastic recovery and wash resistance, but since it is affirmatively emulsified, the stability of the emulsion is extremely poor. Thus, emulsions of this type are difficult to store for long periods of time. Moreover, most of the emulsions of this type gum-up whereby they adhere in mass to mangle rolls or the fibrous products during treatment.